When I noted a while back the Mets' good performance against good teams (they are now 21-15 against teams over .500, and looked even better than that before the D-Backs dropped below the line), one of the chief contributors to that split personality has been Olver Perez, as has become even more pronounced with outstanding starts against the Yankees and Phillies, against whom he's a combined 3-0 with an 0.82 ERA in 5 starts. Here's Perez's line against winning vs. non-winning teams:

Winning (10 starts): 5-0, 2.74 ERA, 6.64 H, 1.01 HR, 3.75 BB, 8.09 K/9, 6.2 IP/Start
Losing (8 starts): 1-5, 7.97 ERA, 10.02 H, 2.31 HR, 7.20 BB, 6.69 K/9, 4.4 IP/Start

It's hard not to conclude from this, as from his performance in the 2006 NLCS, that Perez' problem in very large measure is his inability to focus on what he's doing when the pressure is off.